O-GalNAc glycans enrich in white matter tracts and regulate nodes of Ranvier

Protein O-glycosylation is a critical modification in the brain, as genetic variants in the pathway are associated with both common and severe neuropsychiatric phenotypes. However, little is known about the most abundant type of O-glycan in the mammalian brain, which are O-GalNAc linked. Here, we determined the spatial localization, protein carriers, and cellular function of O-GalNAc glycans in mouse brain. We observed striking spatial enrichment of O-GalNAc glycans in white matter tracts and at nodes of Ranvier. Glycoproteomic analysis revealed that more than half of the identified O-GalNAc glycans were present on chondroitin sulfate proteoglycans termed lecticans, and display both domain enrichment and site-specific heterogeneity. Though genetic ablation in a single cell type failed to replicate the severe phenotypes seen in congenital disorders, inhibition of O-GalNAc synthesis in neurons reduced binding of Siglec-4, a known regulator neurite growth, and shortened the length of nodes of Ranvier. This work highlights a new function of O-GalNAc glycans in the brain and will inform future studies on their role in development and disease.